The invention relates to a method of manufacturing a semiconductor device whereby a layer comprising aluminium is deposited by means of a sputter deposition process on a surface of a semiconductor body which is placed on a holder in a reaction chamber.
The layer comprising aluminium may be a layer of pure aluminium, but alternatively a layer of aluminium to which up to a few percents of a different element, such as silicon or copper, have been added. It is also possible for more elements, such as both silicon and copper, to be added. Such additives serve to improve the properties of the aluminium layer.
The surface of a semiconductor body is in general not plane, but contains stepped structures which in practice may have, for example, a step height of 1 .mu.m and a step width of 2 .mu.m. Such structures then are, for example, contact holes having a diameter of 2 .mu.m formed in an insulating layer of 1 .mu.m thickness provided on the surface, or insulated conductor tracks having a height of 1 .mu.m and a width of 2 .mu.m provided on the surface at a mutual interspacing of 2 .mu.m. These stepped structures in practice have side faces which it is comparatively difficult to cover with a layer comprising aluminium.
Methods of the kind mentioned above are known from S. Wolf and R. N. Tauber, "Silicon Processing for the VLSI Era", Lattice Press, vol. I, Process Technology, pp. 368-372, whereby the semiconductor body is heated in order to obtain a better step coverage.
It is found in the deposition of a layer comprising aluminium that a layer is formed on the side faces which has a thickness much smaller than the thickness of the rest of the layer. If a layer having a thickness of approximately 0.5 .mu.m is deposited on a structure having the dimensions mentioned above by way of example, a layer is formed on the side faces of the stepped structures which has a thickness of no more than a quarter of this value. The process then has a step coverage (=ratio of the minimum thickness of the layer on the side faces to the thickness of the rest of the layer) of less than 25%. These differences in thickness will be greater in structures having smaller dimensions, so that the step coverage will thus be smaller. It is desirable, accordingly, to develop a process which provides a better step coverage.
The step coverage is not improved in practice by the said heating of the semiconductor body. A layer deposited in this way in addition shows a comparatively rough surface and a comparatively coarse-grained structure.